First-principles study of bulk ordering and surface segregation in Pt-Rh binary alloys
First-principles study of bulk ordering and surface segregation in Pt-Rh binary alloys
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DOI：
10.1103/physrevb.74.174202
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发表时间：
2006-11
影响因子：
3.7
通讯作者：
Koretaka Yuge;Atsuto Seko;A. Kuwabara;F. Oba;I. Tanaka
中科院分区：
文献类型：
--
作者：
Koretaka Yuge;Atsuto Seko;A. Kuwabara;F. Oba;I. Tanaka
将团簇展开技术与第一性原理计算相结合，用于蒙特卡罗模拟，得到了铂-Rh合金的体相和(111)面的构型热力学。晶格动力学计算表明，振动对PtRh体相稳定性的贡献可以忽略不计。计算得到的体相的短程有序参数、基态和有序转变温度与文献中的实验值符合得很好。计算的(111)面在$T=第1373\Pantom{\Rule{0.3em}{0ex}}\mathrm{K}处的成分分布表明，整个成分在顶层富含铂，在第二层亏损铂，这与实验观察到的结果是一致的。在低温下，${\mathm{pt}}_{25}{\mathm{Rh}}_{75}和${\mathm{pt}}_{50}{\mathrm{rh}}_{50}之间的层成分分布随温度的变化有显著差异。次表层的铂组分与温度呈正相关，而次表层的铂组分在$T\ensuremath{\sim}300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.处有一个最小值前者可以定性地解释为仅考虑现场能量。后者是由于发生了从$(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$有序合金到无序合金的亚层受限相变。
The cluster expansion technique in conjunction with first-principles calculations has been applied in Monte Carlo simulations to derive the configurational thermodynamics of the bulk and (111) surface of Pt-Rh alloys. Lattice-dynamics calculations reveal that the vibrational contribution to Pt-Rh bulk phase stability is fairly negligible. Calculated short-range-order parameter, ground state, and ordering transition temperature ${T}_{c}$ of bulk ${\mathrm{Pt}}_{50}{\mathrm{Rh}}_{50}$ are in satisfactory agreement with experimental values in the literature. Calculated composition profiles of the (111) surface at $T=1373\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ show the enrichment of Pt at the top layer and Pt depleted at the second layer for the entire composition, which is in agreement with experimental observations. At low temperatures, a significant difference is found in the temperature dependence of the layer composition profile between ${\mathrm{Pt}}_{25}{\mathrm{Rh}}_{75}$ and ${\mathrm{Pt}}_{50}{\mathrm{Rh}}_{50}$. While Pt composition of the ${\mathrm{Pt}}_{25}{\mathrm{Rh}}_{75}$ subsurface shows positive temperature dependence, that of ${\mathrm{Pt}}_{50}{\mathrm{Rh}}_{50}$ has a minimum at $T\ensuremath{\sim}300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The former can be qualitatively interpreted by taking account of the on-site energy only. The latter is due to the occurrence of sublayer-confined phase transition from $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ order to disorder alloys.